Fluid and air handling in blood and dialysis circuits

ABSTRACT

An air purging method includes: (a) detecting a low fluid level in a blood circuit indicating a high amount of air in the blood circuit; (b) stopping a blood pump; (c) closing a venous patient line; (d) opening a blood circuit air vent valve and a drain valve; and (e) running the blood pump to meter air through the air vent valve and the drain valve to a drain.

PRIORITY CLAIM

This application claims priority to and the benefit of U.S. ProvisionalPatent Application Ser. No. 60/976,731, filed Oct. 1, 2007, entitled“Fluid And Air Handling In Dialysis Circuit Air Removal System”.

BACKGROUND

The examples discussed below relate generally to medical fluid delivery.More particularly, the examples disclose systems, methods andapparatuses for dialysis, such as hemodialysis (“HD”), hemofiltration(“HF”) hemodiafiltration (“HDF”) automated peritoneal dialysis (“APD”).

Due to various causes, a person's kidneys can fail. Renal failureproduces several physiological derangements. It is no longer possible tobalance water and minerals or to excrete daily metabolic load. Toxic endproducts of nitrogen metabolism (urea, creatinine, uric acid, andothers) can accumulate in blood and tissue.

Kidney failure and reduced kidney function have been treated withdialysis. Dialysis removes waste, toxins and excess water from the bodythat normal functioning kidneys would otherwise remove. Dialysistreatment for replacement of kidney functions is critical to many peoplebecause the treatment is life saving.

One type of kidney failure therapy is Hemodialysis (“HD”), which ingeneral uses diffusion to remove waste products from a patient's blood.A diffusive gradient occurs across the semi-permeable dialyzer betweenthe blood and an electrolyte solution called dialysate to causediffusion. Hemofiltration (“HF”) is an alternative renal replacementtherapy that relies on a convective transport of toxins from patient'sblood. This therapy is accomplished by adding substitution orreplacement fluid to the extracorporeal circuit during treatment(typically ten to ninety liters of such fluid). That substitution fluidand the fluid accumulated by the patient in between treatments isultrafiltered over the course of the HF treatment, providing aconvective transport mechanism that is particularly beneficial inremoving middle and large molecules (in hemodialysis there is a smallamount of waste removed along with the fluid gained between dialysissessions, however, the solute drag from the removal of thatultrafiltrate is not enough to provide convective clearance).

Hemodiafiltration (“HDF”) is a treatment modality that combinesconvective and diffusive clearances. HDF uses dialysate flowing througha dialyzer, similar to standard hemodialysis, to provide diffusiveclearance. In addition, substitution solution is provided directly tothe extracorporeal circuit, providing convective clearance.

Most HD (HF, HDF) treatments occur in centers. A trend towards homehemodialysis (“HHD”) exists today in part because HHD can be performeddaily, offering therapeutic benefits over in-center hemodialysistreatments, which occur typically bi- or tri-weekly. Studies have shownthat a patient receiving more frequent treatments removes more toxinsand waste products than a patient receiving less frequent but perhapslonger treatments. Studies on HHD have shown a reduction inanti-hypertensive medications while restoring normotension. Randomizedtrials on long daily dialysis have shown a reduction in left ventricularhypertrophy, which is a surrogate marker for improved patient survival.In addition a patient receiving more frequent treatments does notexperience as much of a down cycle as does an in-center patient who hasbuilt-up two or three days worth of toxins prior to a treatment,providing much better quality of life. In certain areas, the closestdialysis center can be many miles from the patient's home causingdoor-to-door treatment time to consume a large portion of the day. HHDcan take place overnight or during the day while the patient relaxes,works or is otherwise productive.

Another type of kidney failure therapy is peritoneal dialysis, whichinfuses a dialysis solution, also called dialysate, into a patient'speritoneal cavity via a catheter. The dialysate contacts the peritonealmembrane of the peritoneal cavity. Waste, toxins and excess water passfrom the patient's bloodstream, through the peritoneal membrane and intothe dialysate due to diffusion and osmosis, i.e., an osmotic gradientoccurs across the membrane. Osmotic agent in dialysis provides theosmotic gradient. The spent dialysate is drained from the patient,removing waste, toxins and excess water from the patient. This cycle isrepeated.

There are various types of peritoneal dialysis therapies, includingcontinuous ambulatory peritoneal dialysis (“CAPD”), automated peritonealdialysis (“APD”), tidal flow dialysate and continuous flow peritonealdialysis (“CFPD”). CAPD is a manual dialysis treatment. Here, thepatient manually connects an implanted catheter to a drain to allowspent dialysate fluid to drain from the peritoneal cavity. The patientthen connects the catheter to a bag of fresh dialysate to infuse freshdialysate through the catheter and into the patient. The patientdisconnects the catheter from the fresh dialysate bag and allows thedialysate to dwell within the peritoneal cavity, wherein the transfer ofwaste, toxins and excess water takes place. After a dwell period, thepatient repeats the manual dialysis procedure, for example, four timesper day, each treatment lasting about an hour. Manual peritonealdialysis requires a significant amount of time and effort from thepatient, leaving ample room for improvement.

Automated peritoneal dialysis (“APD”) is similar to CAPD in that thedialysis treatment includes drain, fill and dwell cycles. APD machines,however, perform the cycles automatically, typically while the patientsleeps. APD machines free patients from having to manually perform thetreatment cycles and from having to transport supplies during the day.APD machines connect fluidly to an implanted catheter, to a source orbag of fresh dialysate and to a fluid drain. APD machines pump freshdialysate from a dialysate source, through the catheter and into thepatient's peritoneal cavity. APD machines also allow for the dialysateto dwell within the cavity and for the transfer of waste, toxins andexcess water to take place. The source can include multiple steriledialysate solution bags.

APD machines pump spent dialysate from the peritoneal cavity, though thecatheter, and to the drain. As with the manual process, several drain,fill and dwell cycles occur during dialysis. A “last fill” occurs at theend of APD and remains in the peritoneal cavity of the patient until thenext treatment.

In any of the above modalities, entrained air and other gases are aconcern. Entrained air can cause inaccuracies when pumping dialysate foreither PD or HD. Entrained air can cause a reduction in effectivesurface area in a hemodialysis filter when it accumulates on the filterfibers, leading to a reduction in the effectiveness of the therapy.Entrained air entering a patient's peritoneum during PD can causediscomfort. Entrained air entering a patient's bloodstream during HD canhave severe consequences. Even though the patient may be protected froman air embolism in some HD equipment, there have been situations withremoving the air from the blood in which the patient has had to throwaway the extracorporeal circuit, resulting in blood loss and cost.Accordingly, a need exists to provide an apparatus that ensures thatentrained air is removed from dialysate or blood prior to deliveringsuch fluids to the patient.

SUMMARY

The present disclosure may employ level sensing and coordinated pumpingand valving algorithms to control the fluid level in an air trap. Inaddition, the present disclosure allows the system to flow either gas orfluid (saline and/or heparin and/or priming solution and/or dialysissolution and/or blood and/or etc.) out of a fluid circuit directly to afluid drain and/or fluid vessel (i.e. saline bag and/or priming bagand/or dialysis solution bag and/or container). Also, the presentdisclosure allows the system to flow gas out of a fluid circuit directlyto atmosphere and fluid (saline and/or heparin and/or priming solutionand/or dialysis solution and/or blood and/or etc.) out of a fluidcircuit directly to a fluid drain and/or fluid vessel (i.e. saline bagand/or priming bag and/or dialysis solution bag and/or container).

The method of controlling level and removing air described above hasadvantages in the areas of priming and air trap level control. Currentlyair trap level control is a manual process. Prior to the therapy, theoperator must connect a port on the air trap to a luer connection on theinstrument. This port connects the air trap to a compressor on theinstrument. This in turn allows for lowering or raising the air trapfluid level through level control switches on the instrument. If theoperator does not make this connection securely, blood can flow upthrough this port and into the instrument during the therapy placing thepatient at risk for blood loss and/or blood contamination. In otherdevices the patient attaches a syringe to the extracorporeal circuit totry to draw air out of the circuit. Because of the pressurization of thecircuit blood loss can occur if the tubing is not closed properly afterwithdrawing air and there is also the risk of blood contamination duringthe manual procedure. The present disclosure eliminates these risksbecause the level control mechanism does not require the operator tomake any connections.

During prime, the operator must monitor the fluid level in the air trapand manually raise this level to remove air from the extracorporealcircuit. During therapy, the operator must continue to monitor the fluidlevel in the air trap. If the operator fails to properly maintain thefluid level and lets this level drop to where air is able to passthrough the air trap the patient is at risk for an air embolism. The airtrap level changes with changes in fluid pressure, making frequentmonitoring of the fluid level in the air trap important. The presentdisclosure removes both of those failure causes by using automatic levelsensing to determine when action needs to be taken to raise the leveland uses pump and valve configurations to automatically purge the air.

In addition, the present disclosure allows the priming solution from theextracorporeal circuit to be dumped to the drain. Currently the primingsolution is either returned to the patient or purged to a wastecontainer. Each of these methods have risks. If the priming solution isreturned to the patient, it may return harmful substances that werereleased from the disposable kit and/or dialyzer during the prime, tothe patient. If the priming solution is sent to a waste container, thereis a risk that the patient may lose a significant amount of blood if theoperator does not stop the purge at the appropriate time. With thecurrent method of sending prime solution to a waste container, theoperator connects the arterial bloodline to the patient's arterialaccess site. The venous line remains disconnected while the instrumentdraws blood from the patient and displaces priming fluid from the venousline into a waste container or rinse bucket. If the operator fails tostop the blood pump and connect the venous line to the patient whenblood reaches the end of the venous bloodline, significant blood lossmay result.

It is accordingly an advantage to provide improved systems and methodsfor the removal of air from dialysis systems.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1 to 5 illustrate various steps for a method and correspondingsystem for venting air to drain.

FIGS. 6 to 12 illustrate various steps for a method and correspondingsystem for venting air to atmosphere.

FIGS. 13 to 18 illustrate various steps for a method and correspondingsystem for venting air to a bag, such as a saline bag.

DETAILED DESCRIPTION

The systems described herein include common components (unless otherwisestated), such as the following dialysate valves: V-AVD-P, which is aprimary dialysate air vent valve; V-AVD-S, which is a secondary air ventvalve; V-BI, which is a balance chamber or balance tube inlet valve;V-B1-FI, which is a balance chamber 1 fresh inlet valve; V-B1-FO, whichis a balance 1 fresh outlet valve; V-B1-SI, which is a balance chamber 1spent inlet valve; V-B1-SO, which is a balance chamber 1 spent outletvalve; V-B2-FI, which is a balance chamber 2 fresh inlet valve; V-B2-FO,which is a balance chamber 2 fresh outlet valve; V-DD, which is adialysate drain valve; V-DR, which is a dialysate recirculation valve;V-DBY, which is a dialyzer bypass valve; V-DI-PRE, which is adialysate/infusate predilution hemofiltration or hemodialfiltrationvalve; V-DI-VEN, which is a dialysate/infusate postdilutionhemofiltration or hemodialfiltration valve; V-DI-FIL, which is adialysate/infusate inlet to the filter, and V-AV, which is an airlinevent valve.

Common blood valves (unless otherwise stated) include V-AVB-P, which isa primary blood vent valve; V-AVB-S, which is a secondary blood ventvalve; V-SA, which is a saline to arterial side of blood circuit valve;V-SV, which is a saline to venous side of blood circuit valve; and V-H,which is a heparin valve.

The above valves are all volcano or cassette type valves in oneembodiment (pneumatically or electromechanically actuated). Thefollowing valves can instead be pinch valves or clamps: V-DB1 throughV-DB6, which open and close supply lines to solution bags 1 to 6,respectively; V-ALC, which is an arterial Line clamp (fail safe); andV-VLC, which is a venous line clamp (fail safe).

The systems each include temperature sensors, such as: T-DC, which is adialysis solution preheat temperature sensor; and T-DH, which is adialysis solution heated temperature. The systems each include pressuresensors, such as: P-DO, which senses a pressure of fluid leaving thedialyzer or filter; P-AL, which is an arterial line pressure sensor;P-VL, which is a venous line pressure sensor; P-PPB, which is a postblood pump pressure sensor.

The systems each include optical sensors, such as: for balance chamber1, O-B1-T1, transmitter 1 transmits to O-B1-R1, receiver 1 for end oftravel; O-B1-T2, transmitter 2 transmits to O-B1-R2, receiver 2 for endof travel; O-B1-T3, transmitter 3 transmits to O-B1-R3, receiver 3 forend of travel; O-B1-T4, transmitter 4 transmits to O-B1-R4, receiver 4for end of travel. Balance chamber 2 has the same set of end of traveloptical sensors. O-HT1 is a heparin transmitter that transmits to O-HR1,heparin receiver to look for heparin instead of blood.

The systems each include other sensors, such as: CS 1 to 12, which arecapacitive sensors for sensing the presence and/or orientation of thesolution bags. AD-AL, which is an arterial line, e.g., ultrasonic, airdetector. AD-VL, which is a venous line, e.g., ultrasonic, air detector.AD-HL, which is a heparin line, e.g., ultrasonic, air detector. BSD-VL,which is a venous line blood/saline, e.g., optical, detector. L-ATD,which is a dialysate air trap level sensor. L-ATB, which is a blood airtrap level sensor. BLD, which is an e.g., optical, blood leak detector.ADS-A, which is an arterial line access disconnection sensor. ADS-V,which is a venous line access disconnection sensor.

The systems also include a drain relief valve RV-Drain and check valvesCK-ATB for blood air trap, CK-PRE for prefilter infusate and CK-VEN forvenous infusate.

The systems also include a filter, F-VL, which is a venous linemacro-aggregate filter and other components such as ATD, which is adialysate air trap and ATB, which is an air trap for blood.

The above valves and sensing areas for the above sensors can be placedin one or more disposable pumping cassette. For example, the systems canemploy dedicated blood and dialysate cassettes with integrated airtraps. Suitable configurations for cassettes with air traps aredisclosed in co-pending patent application Ser. No. 11/865,577, entitled“Dialysis Systems Having Air Traps With Internal Structures To EnhanceAir Removal”; Ser. No. 11/865,583, entitled “Dialysis Systems Having AirSeparation Chambers With Internal Structures To Enhance Air Removal”;Ser. No. 11/865,552, entitled “Dialysis System Having Air SeparationChambers With Internal Structures To Enhance Air Removal”; and60/976,731, entitled “Fluid And Air Handling In Dialysis Circuit AirRemoval System”, each filed on Oct. 1, 2007, assigned to the eventualassignee of the present disclosure, the entire contents of each of whichare incorporated expressly herein by reference.

I. Vent to Drain

Referring now to the drawings and in particular to FIGS. 1 to 5, in oneprimary embodiment a dialysis system 10 and corresponding method ventsair to drain. System 10 can accomplish at least two tasks with the ventto drain option: (i) venting air that accumulates in an air trap ATD(air trap for dialysate) or ATB (air trap for blood) during prime orthroughout the course of a therapy and (ii) purging extracorporealcircuit priming solution, e.g., saline, to drain (as opposed toreturning to the solution to the patient).

Vent To Drain—Purging Air That Accumulates During Therapy

The air purging method of system 10 determines in one embodiment when itis necessary to remove air from the air trap, e.g., via an automaticlevel sensor L-ATD or L-ATB associated with air trap ATD and ATB,respectively, or via operator intervention. System 10 begins the airremoval process by establishing an appropriate flow path from air trapATD or ATB. The flow path from air trap ATD to drain 12 will be viadialysate circuit 20. The flow path from air trap ATB to drain 12 willbe via blood circuit 30. Once the relevant flow path is open, system 10displaces air from the air trap ATD or ATB, generating a pressure in theair trap that is higher than the pressure of drain 12. System 10continues to displace air from the air trap ATD or ATB until automaticlevel sensor L-ATD or L-ATB, respectively, senses that it is no longernecessary to do so. Or, an operator visually determines that enough airhas been removed from system 10.

One example of purging air from blood circuit 30 to drain 12 isillustrated in FIG. 1. Here the extracorporeal circuit level detectorL-ATB detects a low fluid level. System 10 stops blood pump (PUMP-Blood)and dialysis solution pumps (PUMP-DF, PUMP-DS). System 10 closes venouspatient line clamp V-VLC, saline valves V-SV, V-SA, heparin valve V-H,and extracorporeal air vent valves V-AVB-S, V-AVB-P in extracorporealcircuit 30. System 10 opens air vent valve V-AV and drain valve V-DDnear drain 12.

System 10 then begins running PUMP-Blood clockwise, while metering airthrough the air vent valves V-AVB-S and V-AVB-P. Air vent valves V-AVB-Sand V-AVB-P alternate in a chamber-lock type manner. First, vent valveV-AVB-P is opened allowing air to pressurize the line up to vent valveV-AVB-S. Then, the valve states are reversed, allowing pressurized airtrapped between the vent valves V-AVB-S and V-AVB-P to be released todrain 12 via air vent line 14. One of the vent valves is thus closed atall times, and the valves alternate at a rate related to the rate ofPUMP-Blood.

The extracorporeal circuit level detector L-ATB may be used incombination with a blood leak detector BLD (see FIG. 5) to ensure thatthe blood level does not fall too low and to detect when the blood levelhas overfilled blood air trap ATB. When blood leak detector BLD detectsan overfill, system 10 stops PUMP-Blood and closes extracorporeal airvent valves V-AVB-S and V-AVB-P, closes air vent valve V-AV, and closesdrain valve V-DD. System 10 then opens venous patient line clamp V-VLCand saline valves V-SV, V-SA or heparin valve V-H if appropriate andrestarts PUMP-Blood to push an appropriate amount of blood from air trapATB to the patient, lowering the level in the air trap, and allowingfluid in vent line 14 sensed at BLD to fall back into blood from airtrap ATB. Dialysis solution pumps DF and DS are also run at the samerates they were running before the air vent to dialyze blood that isbeing pushed through dialyzer 16 during the level lowering processwithin air trap ATB.

Vent To Drain—Purging Extracorporeal Priming Solution to Drain

System 10 begins a blood prime process after extracorporeal circuit 30has been primed with priming fluid (saline, heparin, dialysis solutionetc.). For blood prime, system 10 assures that the patient has beenconnected to the system or accessed. First, system 10 communicatescircuit 30 with patient 18 flow path. System 10 then flows blood frompatient 18, through the circuit 30, including air trap ATB, to displacepriming fluid out of system 10 to the fluid drain 12, until theextracorporeal circuit is sufficiently primed with blood, e.g., using ablood detector BLD and/or flow sensing and/or a recorded number of pumprotations sufficient to completely remove priming fluid and/or a totaltime spent pumping sufficient to completely purge circuit 30 of primingfluid.

FIGS. 1 to 4 illustrate in detail how system 10 performs blood primeventing. In FIG. 1, system 10 performs a first step in which it is in asafe state following extracorporeal circuit prime with all valves andpatient line clamps closed and all pumps stopped.

At step 2 in FIG. 2: (a) an operator establishes vascular access with avenous patient line 32 of blood circuit 30; (b) the operator establishesvascular access with the arterial patient line 34 of blood circuit 30;(c) system 10 prepares for blood prime by opening extracorporeal circuitair vent valves V-AVB-S and V-AVB-P, dialysate circuit air vent valvesV-AVD-S and V-AVD-P, and drain valves V-DD and V-DR; (d) system 10 runsfresh dialysate pump DF in the clockwise direction as shown in FIG. 2until the blood saline detector BSD-VL detects blood. System 10 can alsorun fresh dialysate pump DF longer, so blood moves beyond the bloodsaline detector, e.g., using a total number pump strokes as theindicator to finally stop dialysate pump DF. This operation pulls bloodfrom patient 18, through venous or return line 32, to blood salinedetector BSD-VL, displacing priming fluid in venous line 32 with thepatient's blood. Negative pressure is applied by priming fluid beingpulled through air vent line 14 and blood air trap ATB. Any air ispushed to drain via open valve V-DD.

At step 3 in FIG. 12, system 10 returns to a safe state by closing allblood and dialysate valves and patient line clamps and stopping allpumps.

At step 4 in FIG. 3, system 10 prepares for completion of blood prime byopening extracorporeal circuit air vent valves V-AVB-S and V-AVB-P,dialysate circuit air vent valves V-AVD-S and V-AVD-P, arterial patientline clamp V-ALC, and drain valve V-DD. System 10 starts PUMP-Blood inthe clockwise direction as shown in FIG. 3 and runs the pump for aspecific number of pump strokes or a specific period of time until bloodtravels from patient 18, through arterial line 34, dialyzer 16, and aportion of venous line 32 to blood air trap ATB. System 10 can also runPUMP-Blood longer so blood moves into the air trap ATB, provided system10 can verify that blood does not leave blood air trap ATB during therest of the priming process.

At step 5 in FIG. 1, system 10 returns to a safe state by closing allvalves and patient line clamps and stopping all pumps. All saline hasbeen removed from blood circuit 30 except perhaps for a small amountbetween blood air trap ATB and blood saline detector BSD-VL. Again, anyair is pushed to drain via valve V-DD.

Vent To Drain—Alternative Vent Valving

Referring now to FIG. 4, secondary air vent valves V-AVD-S and V-AVB-Sfor the dialysate circuit 20 and extracorporeal circuit 30,respectively, have been removed to reduce hardware. The vent to drainand priming fluid to drain sequences above may be performed using thereduced vent valve arrangement of FIG. 4. To increase safety, a bloodleak detector BLD may be added to vent line 14 upstream of the singlyused air vent valves V-AVD-P and V-AVB-P. Since system 10 is closed todrain, it may be possible to eliminate both the primary and secondaryvent valves.

Vent To Drain—Extra Blood Detector

Referring now to FIG. 5, to prime the extracorporeal circuit 30 to agreater extent, a blood detector BLD can be placed in the post-air trapair vent line, between trap ATB and vent valve V-AVB-P or alternativelybetween valves V-AVB-P and V-AVB-S. In FIG. 5, dialysate pump DF isshown pulling saline, as described shown in FIG. 2, in turn pullingblood to the added detector BLD. Blood could be drawn alternatively todetector BLD via PUMP-Blood via the process of FIG. 3. An advantage ineither case is that more of the air trap priming volume or saline issent via drain line 14 to drain 12.

Vent To Drain—Fluid Use Efficiency

It is also possible in the vent to drain system 10 embodiments tomaximize fluid use efficiently by pumping dialysis solution to prime theextracorporeal circuit. Here, a suitable path of valves is opened toallow fresh dialysate pump DF to pump fresh dialysate into dialyzer 16,and through the hollow fiber membranes of the dialyzer, intoextracorporeal circuit 30. In this manner, system 10 can remove air fromcircuit 30 to drain using dialysate instead of requiring an extrapriming fluid, such as saline. The dialysate can then be replaced withblood as shown above, so that the dialysate volume is not delivered tothe patient.

II. Vent to Atmosphere

In another primary embodiment shown in FIGS. 6 to 12, the system 10vents air to atmosphere. System 10 can accomplish at least two tasksusing the vent to atmosphere option: (i) venting air that accumulates inthe blood air trap during prime or throughout the course of a therapyand (ii) purging the extracorporeal circuit priming solution to drain(as opposed to returning the priming solution to the patient).

Vent to Atmosphere—Purging Air That Accumulates During Therapy

In the vent to atmosphere embodiment, system 110 determines when it isnecessary to remove air from the extracorporeal or dialysate side airtraps ATD and ATB via automatic level sensors L-ATD and L-ATB and/oroperator intervention as discussed above. System 110 begins the airremoval process by establishing an appropriate flow path from the airtrap ATD or ATB to atmosphere. Once the flow path is open, system 110displaces air from the relevant air trap ATB, generating a higher thanatmospheric pressure in the associated air trap and/or generating alower than air trap pressure in the atmosphere, e.g., drawing a vacuumon the air trap. System 110 continues to displace air from the air trapuntil it is no longer necessary to do so (as determined by automaticlevel sensors L-ATD or L-ATB and/or via operator intervention.

FIG. 6 illustrates an embodiment of system 110 in which venting toatmosphere can be accomplished. System 110 differs form system 10primarily in that system 110 has connected drain vent valve V-AV toatmosphere through a 0.2 micron filter instead of connecting it to thedrain lines as in system 10. All air is vented through dialysate ventvalve V-AV to atmosphere through this filter.

In one sequence, the extracorporeal circuit level detector L-ATB detectsa low fluid level. System 110 stops PUMP-Blood and dialysis solutionpumps DF and DS. System 110 closes venous patient line clamp V-VLC,saline valves V-SV and V-SA, heparin valve V-H, and extracorporeal airvent valves V-AVB-S, V-AVB-P and opens saline valve V-SA. System 110then slowly runs PUMP-Blood clockwise (as oriented in FIG. 6), drawingin blood while metering air through the air vent valves V-AVB-S andV-AVB-P and through open valve V-AV and out the 0.2 micron filter. Oneof the vent valves is closed at all times as described above to ensurethat no outside air contacts blood.

The extracorporeal circuit level detector L-ATB may be used incombination with a blood leak detector BLD (see FIG. 5) to ensure thatthe blood level does not fall too low and to detect when the blood levelhas overfilled blood air trap ATB. When blood leak detector BLD detectsan overfill, system 110 closes extracorporeal air vent valves V-AVB-Sand V-AVB-P, opens venous patient line clamp V-VLC and saline valvesV-SV, V-SA or heparin valve V-H if appropriate and restarts dialysissolution pumps DF and DS and Pump-Blood at the same rates that they wererunning before the venting of air through trap ATB, vent valve V-AV, and0.2 micron filter.

Vent to Atmosphere—Purging Extracorporeal Priming Solution to Drain

System 110 begins a blood prime process after extracorporeal circuit 30has been primed with priming fluid (saline, heparin, dialysis solutionetc.). For blood prime, system 110 assures that the patient has beenconnected to the system or accessed. First, system 110 communicatescircuit 30 with patient 18. System 110 then flows blood from patient 18through the circuit 30, including air trap ATB to displace priming fluidout of system 110 to the fluid drain 12 until the extracorporeal circuitis sufficiently primed with blood, e.g., using a blood detector BLDand/or flow sensing and/or a recorded number of pump rotationssufficient to completely remove priming fluid and/or a total time spentpumping sufficient to purge circuit 30 of priming fluid.

FIGS. 6 to 10 illustrate in detail how system 110 accomplishes bloodprime venting to atmosphere.

In step 1 at FIG. 6, system 110 is in a safe state followingextracorporeal circuit prime with all valves and patient line clampsclosed and all pumps stopped.

In step 2 at FIG. 7: (a) an operator establishes vascular access withthe venous patient line 32; (b) system 110 prepares for blood prime byopening extracorporeal circuit air vent valves V-AVB-S and V-AVB-P,dialysate circuit air vent valves V-AVD-S and V-AVD-P, and drain valvesV-DD and V-DR; and (c) system 110 runs fresh dialysate pump PUMP-DF inthe clockwise direction as seen in FIG. 7 and until the blood salinedetector BSD-VL detects blood. It is also be possible to run the freshdialysate pump DF longer, so blood moves beyond the blood salinedetector BSD-VL using total pump strokes as the indicator to stop, forexample.

In step 3 at FIG. 6, system 110: (a) returns to safe state by closingall valves and patient line clamps and stopping all pumps; and (b) theoperator establishes vascular access with the arterial patient line 34.

In step 4 at FIG. 8: (a) system 110 prepares for blood prime by openingextracorporeal circuit air vent valves V-AVB-S and V-AVB-P, dialysatecircuit air vent valves V-AVD-S and V-AVD-P, and drain valves V-DD andV-DR; (b) system 110 runs PUMP-Blood in the clockwise direction, and thefresh dialysate pump DF in the clockwise direction as shown in FIG. 8 atthe same flow rate for a specific number of pump strokes or period oftime until blood flows through arterial line 34, dialyzer 16, and aportion of venous line 32 until reaching air trap ATB. Pressure sensorP-PPB can be used to indicate when one pump is running at a higher flowrate than the other. It is also possible to run the pumps longer, soblood moves into the air trap, provided that system 110 can verify thatblood never leaves the air trap during the rest of the priming process.A blood-saline-air detector can be installed between V-AVB-P and V-AVB-Sto further optimize priming solution removal.

In step 5 at FIG. 6, system 110 returns to the safe state by closing allvalves and patient line clamps and stopping all pumps.

In step 6 at FIG. 9, system 110 prepares to clear the dialysate circuitside of the air vent by opening the air vent valve V-AV, dialysatecircuit air vent valves V-AVD-S and V-AVD-P, and drain valves V-DD andV-DR.

In step 7 at FIG. 10, system 110 runs the fresh dialysate pump L-ATB-DFin the clockwise direction, pumping fresh fluid from air trap ATB andpulling air into the trap via air vent line 14 and vent valves V-AVD-Sand V-AVD-P until level detector L-ATD in the dialysate circuit air trapATD indicates a certain level. System 110 can alternatively accomplishthis step by running dialysate pump DF for a specific number of pumpstrokes or period of time until fluid is completely removed from thedialysate circuit air vent line 14.

In step 7 at FIG. 10, system 110 runs the fresh dialysate pump L-ATB-DFin the clockwise direction, pumping fresh fluid from line 14 and pullingair into the trap ATD via air vent line 14 and vent valves V-AVD-S andV-AVD-P until level detector L-ATD in the dialysate circuit air trap ATDindicates that there is no fluid in air trap ATD. System 110 canalternatively accomplish this step by running dialysate pump DF for aspecific number of pump strokes or period of time until fluid iscompletely removed from the dialysate circuit air vent line 14.

In step 8 at FIG. 6, system 110 returns to safe state by closing allvalves and patient line clamps and stopping all pumps.

During the therapy, if air gathers in the top of air trap ATB, valvesV-AVB-P and V-AVB-S are alternately opened so that air is shuttled outof the air trap without allowing any blood to escape and vented throughvalve V-AV and the 0.2 micron vent filter.

Vent To Atmosphere—Alternative Vent Valving

Just like with FIG. 4 for venting to drain, system 110 can be modifiedto remove secondary air vent valve V-AVB-S from blood circuit 30 andV-AVD-S from dialysate circuit 20 to reduce hardware, which can also beperformed by adding a blood leak detector BLD in vent line 14 upstreamof the primary vent valves V-AVB-P and V-AVD-P to sense any blood thatmay enter vent line 14. Since venting is done to atmosphere, at least aprimary vent valve should be provided at the blood and dialysate airtraps ATB and ATD.

Vent To Atmosphere—Extra Drain/Air Vent Lines

FIG. 11 illustrates that system 110 can alternatively connect air ventline 14 running from air traps ATB and ATD directly to drain line 12,similar to the vent to drain system 10. Unlike system 10, which providesan extra vent to drain valve V-AV for both air traps, system 110 usesvent valves V-AVD-S and V-AVD-P to control flow from dialysate air trapATD to drain 12. Valve V-AC is provided as a vent valve for blood airtrap ATB, which provides a second vent to atmosphere option using ventvalves V-AVB-S and V-AVB-P and a 0.2 micron filter.

FIG. 12 illustrates that system 110 can alternatively have separate airvent lines for the dialysate and extracorporeal circuits, allowing thecircuits to both vent at the same time. In FIG. 12, dialysate air ventline 14 a runs to drain 12, while blood air trap ATB vents directly toatmosphere via vent line 14 b, valves V-AVB-S And V-AVB-P and a 0.2micron filter.

Vent To Atmosphere—Extra Blood Detector

In an alternative vent air to atmosphere embodiment, to prime theextracorporeal circuit to a greater extent, a blood detector BLD (seeFIG. 5) can alternatively be placed in the post air-trap air vent line14. An advantage here is that more of the air trap fluid priming volumecan be replaced with blood before treatment.

Vent To Atmosphere—Alternative Method

Referring again to FIG. 6, in a further alternative embodiment, vent toatmosphere system 110 maximizes fluid use efficiently by pumpingdialysis solution to prime the extracorporeal circuit 30. Here, asuitable path of valves is opened to allow fresh dialysate pump DF topump fresh dialysate into dialyzer 16, and through the hollow fibermembranes of the dialyzer, into extracorporeal circuit 30. In thismanner, system 110 can remove air from circuit 30 to drain usingdialysate instead of requiring an extra priming fluid, such as saline.The dialysate can then be replaced with blood as discussed above, sothat the dialysate volume is not delivered to the patient.

Vent To Atmosphere—Fluid Use Efficiency

It is also possible in the vent to atmosphere system 110 to use dialysissolution to prime extracorporeal circuit 30 as discussed above with ventto drain system 10.

III. Vent to Saline Bag

In a further alternative primary embodiment shown in FIGS. 13 to 18,system 210 vents to a bag such as a saline bag 36. Here again, system210 can accomplish at least two tasks: (i) venting air that accumulatesin air traps ATB and ATD during prime or throughout the course of atherapy and (ii) purging the extracorporeal circuit priming solution tosaline bag 36 as opposed to returning the solution to patient 18.

Vent To Saline Bag—Purging Air That Accumulates During Therapy

System 210 determines when it is necessary to remove air from air trapATB and ATD (via e.g., automatic level sensors L-ATB and L-ATD and/oroperator intervention). System 210 begins the air removal process to byestablishing an appropriate flow path from the air trap (extracorporealATB, dialysate ATD) to the saline bag 36. Once the flow path is open,system 210 displaces air from the air trap ATB or ATD by generating ahigher than saline bag pressure in the air trap ATB or ATD and/orgenerating a lower than air trap pressure in the saline bag 36. System210 continues to displace air from the air trap ATB or ATD until it isno longer necessary to do so, for example as determined by automaticlevel sensors L-ATB or L-ATD and/or operator intervention.

FIG. 13 illustrates system 210, which vents air to saline bag 36. Whenextracorporeal circuit level detector L-ATB detects a low fluid level offluid within trap ATB, system 210 stops PUMP-Blood and dialysis solutionpumps DF and DS. System 210 closes venous patient line clamp V-VLC,saline valves V-SV, V-SA, heparin valve V-H and extracorporeal air ventvalves V-AVB-S and V-AVB-P.

System 210 then runs Pump-Blood clockwise, while metering air throughthe air vent valves V-AVB-S or V-AVB-P. Either valve V-AVB-S or V-AVB-Pis closed at all times for safety. The valves alternate in a chamberlock manner, which can be cycled at a rate related to the blood pumprate. This action pushes air to saline bag 36.

The extracorporeal circuit level detector L-ATB may be used incombination with a blood leak detector BLD (see FIG. 5) to ensure thatthe blood level does not fall too low and to detect when the blood levelhas overfilled blood air trap ATB. When blood leak detector BLD detectsan overfill, system 210 stops PUMP-Blood, closes extracorporeal air ventvalves V-AVB-S and V-AVB-P, opens venous patient line clamp V-VLC andsaline valves V-SV, V-SA or heparin valve (V-H) if appropriate; and runsPump-Blood and dialysis solution pumps DS and DF at the same rates theywere running before the air vent action. Such action pulls air salinefrom bag 36 into trap ATB, which pushes blood from the trap ATB.

Vent to Saline Bag—Purging Extracorporeal Priming Solution to Drain

The blood prime process of system 210 begins after the extracorporealcircuit has been primed with priming fluid (saline, heparin, dialysissolution etc.). Blood prime assumes that the patient's blood access hasbeen connected to the system. First, system 210 establishes theappropriate flow paths accomplished with the illustrated (FIG. 13)system of valves and clamps. System 210 then flows blood from patient 18through the appropriate flow path (which includes air trap ATB) todisplace priming fluid saline bag 36 to other containers. System 210then switches the flow path to continue to displace priming fluid untilextracorporeal circuit 30 is sufficiently primed with blood. System 210can determine if the blood prime is complete using a blood detector,flow sensing, or a recorded number pump rotations and/or a total timespent pumping. As with system 110, vent to bag system 210 does not needan extra vent valve V-AV provided with system 210. System 210 replacesvent line 14 with saline vent line 44.

FIGS. 13 to 16 illustrate in detail how blood prime venting to salinebag 36 or other bag can be accomplished.

In step 1 at FIG. 13, system 210 is placed in a safe state followingextracorporeal circuit prime with all valves and patient line clampsclosed and all pumps stopped.

In step 2 at FIG. 14: (a) the operator establishes vascular access withthe venous patient line 32; (b) the operator establishes vascular accesswith the arterial patient line 34; (c) system 210 prepares for bloodprime by opening venous patient line clamp V-VLC and saline valve V-SA;and (d) system 210 runs PUMP-Blood in the counterclockwise direction asseen in FIG. 17, pumping blood from patient 18, through venous line 32until the blood saline detector BSD-VL detects blood. System 210 canalternatively run the PUMP-Blood longer so blood moves beyond the bloodsaline detector BSD, e.g., using total pump strokes as the indicator tostop.

In step 3 at FIG. 13, system 210 returns to the safe state by closingall valves and patient line clamps and stopping all pumps.

In step 4 at FIG. 15, system 210 prepares for blood prime by openingextracorporeal circuit air vent valves V-AVB-S and V-AVB-P, dialysatecircuit air vent valves V-AVD-S and V-AVD-P, arterial patient line clampV-ALC, and drain valve V-DD.

In step 5 at FIG. 16, system 210 runs PUMP-Blood in the clockwisedirection for a specific number of pump strokes or period of timepulling blood from patient 18, through arterial line 34, dialyzer 16 anda portion of venous line 32 until blood reaches the beginning of the airtrap ATB. System 210 can alternatively run the PUMP-Blood longer soblood moves into the air trap ATB, provided that system 210 can verifythat blood does not escape air trap ATB during the blood primingprocess. The addition of a blood saline detector BSD as illustrated inFIG. 5 would facilitate this process.

In step 6 at FIG. 13, the system returns to safe state by closing allvalves and patient line clamps and stopping all pumps.

Vent to Saline Bag—Fewer Air Vent Valves

Referring to FIG. 17, secondary air vent valves for the dialysatecircuit V-AVD-S and extracorporeal circuit V-AVB-S have been removed.Primary vent vales V-AVD-P and V-AVB-P function primarily to maintainsafety and may be used in combination with blood leak detectors BLD's ashas been described herein. Since system 210 is closed to saline bag,however, it may be possible to use no vent valves.

Vent to Saline Bag—No Post-Pump Line

Referring again to FIG. 13, system 210 does not need separate pre- andpost-blood pump saline lines (holding V-SV and V-SA) to the saline bag,so the post-pump saline line (holding V-SV) can be removed. Here system210 uses the air trap fluid line 44 to also function as the post-pumpfluid line.

Vent to Saline Bag—Extra Blood Detector

As with system 10 in FIG. 5, to prime the extracorporeal circuit 30 to agreater extent, system 210 can add a blood detector BLD in the postair-trap air vent line running to saline bag 36. An advantage here isthat more of the air trap priming volume can be sent to the saline orother container.

Vent to Saline Bag—Other Container

Referring to FIG. 18, the vent container does not have to be a salinebag 36. Vent line 44 can run instead to a different container, such as aused supply bag or a dedicated vent container.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

The invention is claimed as follows:
 1. A blood priming methodcomprising: (a) running a dialysate pump to pull blood from a patientinto an extracorporeal blood circuit in a first direction and displacinga priming liquid to a drain for a number of pump cycles or for a giventime by flowing the priming liquid through a line connecting theextracorporeal blood circuit to the drain so that the priming liquiddoes not pass through a blood filter; and (b) running a blood pump topull blood from the patient into the extracorporeal blood circuit in asecond direction and displacing the priming liquid to the drain for anumber of pump cycles or for a given time by flowing the priming liquidthrough the line connecting the extracorporeal blood circuit to thedrain so that the priming liquid does not pass through the blood filter.2. The blood priming method of claim 1, which includes at least one of:(i) verifying step (a) has occurred by detecting blood reaching a bloodpresence detector; (ii) attempting to pump blood to an air trap duringstep (b); and (iii) communicating the dialysate pump with theextracorporeal blood circuit via an air vent line.
 3. A blood primingmethod comprising: (a) running a dialysate pump to pull blood from apatient venous access into an extracorporeal blood circuit in a firstdirection and displacing a priming liquid to a dialysate circuit for anumber of pump cycles or for a given time, the priming liquid flowingthrough a line connecting the extracorporeal blood circuit to thedialysate circuit to bypass a blood filter to reach the dialysatecircuit; and (b) running a blood pump to pull blood from the patientarterial access into the extracorporeal blood circuit in a seconddirection and displacing the priming liquid to the dialysate circuit fora number of pump cycles or for a given time, the priming liquid flowingthrough the line connecting the extracorporeal blood circuit to thedialysate circuit to bypass the blood filter to reach the dialysatecircuit.
 4. The blood priming method of claim 3, which includes at leastone of: (i) verifying step (a) has occurred by detecting blood reachinga blood presence detector; and (ii) attempting to pump blood to an airtrap during step (b).
 5. The blood priming method of claim 3, whichincludes displacing the priming liquid to a drain for at least one of(a) and (b).
 6. The blood priming method of claim 3, wherein the line isan air vent line.